Ignition circuit monitoring for ignition systems is already known in which a sensor signal is generated by an ignition current sensor when each ignition takes place, this sensor signal being stored in a memory and read out after each ignition. The memory content is reset, in turn, after each subsequent ignition, so that an ignition failure is recognized when there is no sensor signal. This ignition circuit monitoring, however, offers no possibility of detecting the frequency of misfirings or the loading of the ignition system due to misfirings. Thus, for example, a single misfiring which is then followed by a very large number of proper ignitions is negligible, but it is disadvantageous when the number of misfirings equals the number of proper ignitions.